Dedent on curly braces on other blocks like for

Based on rust.kak
Fix rust-lang#421

indent/rust.vim

@@ -142,9 +142,8 @@ function GetRustIndent(lnum)
     let l:standalone_close = line =~# '\V\^\s\*}\s\*\$'
     let l:standalone_where = line =~# '\V\^\s\*where\s\*\$'
     if l:standalone_open || l:standalone_close || l:standalone_where
-        " ToDo: we can search for more items than 'fn' and 'if'.
         let [l:found_line, l:col, l:submatch] =
-                    \ searchpos('\<\(fn\)\|\(if\)\>', 'bnWp')
+                \ searchpos('\<\(impl\)\|\(fn\)\|\(struct\)\|\(enum\)\|\(union\)\|\(if\)\|\(for\)\>', 'bnWp')
         if l:found_line !=# 0
             " Now we count the number of '{' and '}' in between the match
             " locations and the current line (there is probably a better